The hydroformylation technique, also known as the “Oxo synthesis”, has been one of the largest homogeneous reactions in the industrial sector since it was discovered by Often Roelen in 1938 (Chem. Abstr. 1944, 3631). Each year, various aldehydes and alcohols produced from Fe, Zn, Mn, Co, Cu, Ag, Ni, Pt, Pd, Rh, Ru and Ir based catalysts have been over 10 million tons. In these catalytic reactions, the ability to achieve high selectivity of linear products (i.e. high linear (normal) to branch (normal) ratio, or l/b) is extremely important for industrial applications. Although large-scale chemical companies and research institutes such as BASF, Dow, Shell, Eastman, LIKAT (Leibniz Institute for Catalysis) and etc. have reported and patented such catalytic reactions in a large amount, linear selectivity is still a practical problem to be solved. New theories and methods for controlling linear selectivity are crucial for hydroformylation reactions. In particular, catalysts with high linear selectivity can produce chemicals in a more environmentally friendly manner under mild conditions.
In industrial hydroformylation reactions, cobalt catalysts (e.g. HCo(CO)4) are in a dominant position until the advent of rhodium catalyst (e.g., HRh(CO)2(PPh3)3) in the 1970s. In 2004, it was estimated that approximately 75% of the hydroformylation reactions worldwide were based on a rhodium-triarylphosphine catalyst system. The efficient selectivity of linear aldehyde products is critical in hydroformylation and its related reactions. The aldehyde product is also an important intermediate in addition to chemicals such as perfumes. The further obtained aldehydes can be further hydrogenated, oxidized and animated to be converted into alcohols, carboxylic acids and amines, and used in bulk chemicals, plasticizers, detergents, surfactants, various solvents, lubricants, coatings and other optical materials, etc.
The HRh(CO)(PPh3)2 catalytic system (J. Org. Chem., 1969, 34, 327-330) invented by Pruett and Smith at Union Carbide coordinates rhodium with an excess amount of phosphine ligands, to form an active and selective hydroformylation species and successfully commercialized. The HRh(CO)(PPh3)2 catalytic system requires a large amount of phosphine ligand because the Rh-PPh3 complex is easily decomposed in the catalytic system, and triphenylphosphine (PPh3) lost from HRh(CO)(PPh3)2 will turn the complex into more active but less selective complexes: HRh(CO)2(PPh3) and HRh(CO)3. Therefore, taking 1-hexene as an example, in industrial process, it is necessary to use up to 820 times excess of PPh3 to Rh to ensure higher selectivity of linear to branched aldehyde products, wherein the selectivity is up to 17:1. In addition, the industrial reaction of propylene uses a 400 times excess of PPh3 to Rh, and the ratio of linear to branched aldehyde products is 8 to 9:1.
In the hydroformylation process, it is important to use less expensive starting materials as reactants. For example, 2-octene and 3-octene are ideal starting materials for the conversion of long-chain internal olefins to linear aldehydes. Raffinate II (a mixture of butenes and butane) or a mixture of 1-butene and 2-butenes are the starting material commonly used in industrial hydroformylation reactions. Furthermore, the hydroformylation reaction of an olefin with functional groups such as a hydroxyl group (—OH) and a carboxyl group (—COOH) is also extremely important. For example, the hydroformylation of propylene alcohol and the subsequent reduction can produce 1,4-butanediol, which is an important raw material for synthetic polymers and other derivatives. In addition, functionalized internal olefins can be used as another synthetic route for difunctionalized building blocks in polymer synthesis. For example, the product produced by the hydroformylation of methyl 3-pentenoate is a raw material in the synthesis of polyamides and polyesters. In isomerization and hydroformylation reactions, high isomerization rate combined with high selectivity to form terminal aldehyde is an ideal reaction process, which not only reduce unnecessary hydrogenation, but also reduce the probability of isomerization to other conjugated compounds.
Many hydroformylation processes still utilize PPh3 as ligands. Although the rhodium/triphenylphosphine system has been successfully implemented in factories all over the world, it limits the ratio of normal to isomeric (n/i) aldehyde products to about 10:1. In addition, the large amount of PPh3 is not only poorly selective in the hydroformylation reaction, but also difficult in separation and posttreatment. In order to tackle these problems, transition-metal-bisphosphorous chelate complexes have been reported and patented by research groups and companies throughout the world. For example 2,2,-bis((diphenylphosphino)methyl)1,1-biphenyl (Bisbi) invented by Eastman; 6,6′-[3,) 3′-di-tert-butyl-5,5′-dimethoxy-1,1′-diphenyl-2,2′-diyl)bis(oxy)]bis(dibenzo[D,F][1,3,2]diphophos) (Biphephos) by Union Carbide (Buckwald); 4,5,-bisdiphenylphosphino-9,9-dimethylxanthene (Xantphos) and bidentate Diphosphoramidite by van Leeuween; 2,2′-bis((diarylphosphino)methyl)-1,1-binaphthyl (Naphos) by Matthias Belter and etc. The structures of these bidentate phosphorus ligands are illustrated as follows:

Using the above bidentate phosphorous ligand, a 400 times excess of PPh3 can typically be reduced to only a 5 times excess of the chelated bidentate phosphorous ligand. This chelated bidentate phosphorous ligand has higher n/i (or l/b) ratio and catalytic activity in the hydroformylation reaction. For example, the n/i ratio of 1-hexene hydroformylation can be up to 70 to 120:1. Casey and van Leeuwen reported that the high selectivity with bisphosphorous ligand is due to the formation of a large bite angle (120 degree) between transition metal and ligand, i.e. The “Bite angle” theory, the structure is illustrated as follows:

Although there are many reports on the use of bidentate phosphorous ligands for hydroformylation reactions, the development of higher selectivity and activity phosphorous ligands has been a research hotspot in the field of hydroformylation. However, it is difficult to achieve high normal to iso products (n/i) ratio due to the detachment of phosphorus during the coordination process of Rh-phosphorous complex and carbon monoxide molecule. Therefore, the development of multidentate phosphorous ligand with multi-chelating and coordination abilities is of great importance.
In addition to high selectivity, high isomerization speed is also a very important factor for the hydroformylation of internal olefins. The isomerization catalyst used in the present invention: Carbonylchlorohydrido[6-(di-tert-butylphosphinomethyl)-2-(N,N-diethylaminomethyl)pyridine] ruthenium(II), also known as Milstein Catalyst, its synthesis method and route was reported by the David Milstein (J. Am. Chem. Soc., 2005, 127, 10840-10841). S. Perdriau et al. (Chem. Eur. J., 2014, 47, 15434-15442) reported the use of RuH(Cl)(PNN)(CO) catalysts for isomerization of terminal olefins to internal olefins. These are the few reports on the isomerization of olefins with RuH(Cl)(PNN)(CO) catalyst Besides, there are few literatures on isomerization and hydroformylation to prepare linear aldehydes with rhodium-ruthenium dual metals.
Taking the 2-octenes hydroformylation as example, the Xantphos type ligand reported by van Leeuwen has a normal to iso products (n/i) ratio of 9.5 (Angew. Chem. Int. Ed, 1999. 38, 336). Beller reported a normal to iso products (n/i) ratio up to 10.1 with Naphos-type ligand (Angew. Chem. Int. Ed., 2001, 40, 3408). The linear selectivity of ortho-phosphonate ligand in the octene mixture was 2.2 claimed by Börner (Angew. Chem. Int. Ed., 2001, 40, 1696). The phosphinate ligands of Union Carbide Corp. (now Dow) have a normal to iso products ratio of: n/i=19 and 17 for 2-hexene and 2-octene respectively (U.S. Pat. No. 4,769,498). All literatures and patents mention above used rhodium as single metal catalyst.
The biphenyl tetradentate phosphine ligand (Tetrabi) used in the present invention has multiple chelating modes owing to its coordination ability. The hydroformylation of internal olefins is carried out in multi-chelating coordination modes with Rh-Tetrabi complex. Phosphine ligands are less likely to decompose from the Rh-Tetrabi catalyst system, and the steric hindrance effect of phosphines inhibits the formation of the isomeric aldehyde product, so that a high normal to iso products ratio is easily obtained. Therefore, the present invention utilizes a dual rhodium-ruthenium transition dual metals and metal-biphenyl tetradentate phosphine ligand as a catalytic system to obtain an unprecedented high normal to iso products ratio in the isomerization and hydroformylation of long-chain internal olefins.